Use of the installed twisted pair telephone network to provide transmission facilities for broadband signal transmission has been suggested in the prior art. Asymmetric digital subscriber line (ADSL) systems take advantage of the existing twisted-pair copper loop that currently provides customer access to the telephone network. ADSL systems are described in an article entitled "ADSL: A New Twisted-Pair Access to the Information Highway", Kyees et al., IEEE Communications Magazine, April 1995, pages 52-59.
In such a system, an ADSL modem is placed at each end of a loop to create a high speed access link in a frequency range above the existing telephone service. ADSL standards specify a high speed simplex channel which provides a downstream data rate of up to 6 megabits/second (mb/s). The downstream channel can be divided into a number of subchannels, if desired. A 64 kilobits/second duplex data channel is associated with the high-speed channel to allow interactive control and information flow between a subscriber and an information service provider. All of this signal bandwidth rides over the 0 to 4 kHz band allotted to basic telephone services.
Through the use of filters, ADSL channels and the telephone channel are maintained separate. At the subscriber location, a splitter diverts the telephone service to the telephone handset, allowing the broadband signals to be received by an ADSL terminal unit which further distributes the broadband signals to various receiving units, such as set-top boxes, computer terminals and other devices. Separate wiring is utilized for connection between an ADSL terminal unit and its respective destination devices.
Because the broadband services are delivered from a centrally located provider to individual subscribers over potentially long distance, twisted pair circuits, ADSL requires sophisticated modems to be used at the receiving ends to cope with variable levels of signal degradation. Such modems are expensive, yet are necessary to assure high quality broadband signal reception at the subscriber. Further, service personnel are required to install special wiring at the subscriber's premises to enable distribution therein of the broadband signals.
In addition to the ADSL system, others have described various techniques and systems for enabling broadband distribution to subscribers connected to the existing twisted pair telephone network. U.S. Pat. No. 4,885,747 to Foglia, entitled "Broadband and Baseband LAN", describes a point-to-point communication system wherein a frequency coupler circuit accepts both baseband and broadband signals and concentrates those signals onto one end of a length of shielded twisted pair conductors. A second frequency coupler is coupled to the opposite end of the shielded twisted pair and separates and distributes the broadband and baseband signals to respective connected ports to which utilization devices are connected. At those ports, "lobe" assembly devices provide interface functions for each particular attached machine, or group of machines.
U.S. Pat. No. 5,255,267 to Hansen et al., entitled "Apparatus for Combining Broadband and Baseband Signal Transmissions" combines such signals in a baseband distribution cable for transmission to various user devices. The broadband signal is split into a plurality of segments, each segment supported by a baseband repeater. Filters prevent interference with the baseband signals in each segment and provide a high impedance to the baseband signals. The system is described in the context of an Ethernet network.
U.S. Pat. No. 5,499,241 to Thompson et al., entitled "Broadband Communication System" describes a system for coupling telephony or other digital networks to a cable television network. The system transmits multiple telephony signals in 3 MHz channels in a forward band of the cable TV network. Audio and control signals returning from the subscriber are digitized under telephony signals and modulated on a 50 kHz carrier that is used for reverse direction transmissions. U.S. Pat. No. 5,363,432 to Martin et al., entitled "Transmission of Broadband Signals to Subscribers Using a Telecommunications Cable" describes a method of transmitting a broadband signal to a subscriber residence, wherein the broadband signal is coupled between a shield and one of the conductors of a pair of conductors.
U.S. Pat. No. 5,387,927 to Look et al., entitled "Method and Apparatus for Broadband Transmission from a Central Office to a Number of Subscribers" describes the forming of multiple channels of digital signals and modulating a plurality of carrier signals therewith. The resultant modulated channels are multiplexed to form a combined signal which is then used to modulate a laser light beam. The modulated light beam is transmitted over a light fiber to local distribution boxes. There, the modulated signals are converted to electrical signals and are broadcast to subscriber devices.
The above-described prior art requires either: expensive modems for receipt of broadband signal which have travelled over long distance twisted pair links; installation of dedicated wiring within the subscriber's premises; or installation of entirely new transmission facilities to enable transmission of both baseband and broadband signals.
Accordingly, it is an object of this invention to provide a system for distributing broadband services over the existing, twisted pair, non-shielded telephone network.
It is a further object of this invention to provide a facility for transmission and receipt of broadband signals over the installed telephony network, wherein already present wiring in a subscriber facility is used for interconnection of the broadband signals to subscriber devices.
It is yet another object of this invention to provide a broadband distribution system which uses the installed telephony network and wherein added broadband facilities are transparent to baseband telephone signals.
It is still another object of this invention to utilize the installed twisted pair telephony network for transmission of broadband signals, wherein signal routing is substantially independent of pre-existing twisted pair circuit paths.